This application claims priority under 35 U.S.C. xc2xa7119 to Japanese Application Ser. No. 2000-346526, filed Nov. 14, 2000, and to Japanese Application Ser. No. 2000-384120, filed Dec. 18, 2000, both applications are hereby incorporated herein by reference.
This invention relates to electrochemical fuel cells and methods for making an electrochemical fuel cell. More particularly, the present invention is directed to a fuel cell system having electrodes incorporating hydrogen storable substances, such as fullerenes, carbon nanotubes, carbon nanohorns, carbon nanofibers and metal encapsulated fullerenes.
Fuel cells combine hydrogen and oxygen without combustion to form water and to produce direct current electric power. The process can be described as electrolysis in reverse. Fuel cells have potential for stationary and portable power applications; however, the commercial viability of fuel cells for power generation in stationary and portable applications depends upon solving a number of manufacturing, cost, and durability problems.
Electrochemical fuel cells convert fuel and an oxidant to electricity and a reaction product. A typical fuel cell consists of a membrane and two electrodes, called a cathode and an anode. The membrane is sandwiched between the cathode and anode. Fuel, in the form of hydrogen, is supplied to the anode, where a catalyst, such as platinum and its alloys, catalyzes the following reaction: 
At the anode, hydrogen separates into hydrogen ions (protons) and electrons. The protons migrate from the anode through the membrane to the cathode. The electrons migrate from the anode through an external circuit in the form of electricity. An oxidant, in the form of oxygen or oxygen containing air, is supplied to the cathode, where it reacts with the hydrogen ions that have crossed the membrane and with the electrons from the external circuit to form liquid water as the reaction product. The reaction is typically catalyzed by the platinum metal family. The reaction at the cathode occurs as follows: 
Thus, the fuel cell generates electricity and water through the electrochemical reaction.
In a known hydrolysis cell, a cationic membrane is positioned between platinum containing electrodes. In such a hydrolysis cell, the following electrochemical reactions occur: 
The most promising fuel cells for widespread transportation use are Proton Exchange Membrane (PEM) fuel cells. PEM fuel cells operate at relatively low temperatures, have a relatively fast response time and have relatively high energy density compared to other fuel cell technologies. Current PEM fuel cells rely on flat-plate electrodes. Any fuel cell design should: (a) allow for supply of the reactants (typically, hydrogen and oxygen); (b) allow for mass transport of the reaction product (water) and associated inert gases (nitrogen and carbon dioxide from air); and (c) provide electrodes to support the catalyst, to collect electrical charge, and to dissipate heat. Electrical and thermal resistance, reactant pressures, temperatures, surface area, catalyst availability are some of the major factors affecting the performance and efficiency of a fuel cell. Some problems encountered in the use of PEM fuel cells include the need to reduce thermal stress concentrations, and the need to increase integrity and performance of the fuel cell.
In recent years, new xe2x80x9cnanoxe2x80x9d carbon materials have being produced, and they may be considered as the future storage material of hydrogen for a new generation energy producing and storage devices. However, it is difficult to put compressed hydrogen in a container constructed from such xe2x80x9cnanoxe2x80x9d carbon materials. For example, certain hydrogen storable substances, such as a carbon nanotube or a carbon nanofiber, have a storage capacity of about ten kilograms/meter3 (kg/m3). Since the chargeable ratio is about fifty percent, then the actual stored hydrogen is five kg/m3. Especially for the use of hydrogen fuel cells in automobiles, airplanes and other moving transports, it is necessary to safely store hydrogen, so as to avoid hydrogen combustion in the fuel cell. In addition, a system is needed to quickly supply hydrogen to the fuel cell anode.
When hydrogen storable metal compounds are used, repeated input and output of hydrogen leads to degradation of the compound. Further, the mass ratio of the storable hydrogen to the metal used is very low. Consequently, when the hydrogen storable metal compounds contain precious metals, such as platinum, the cost is prohibitively high, and thus, not suitable of such fuel cells for most applications of the technology.
What has been needed and heretofore unavailable is a safe, efficient and cost effective fuel cell, which is suitable for mass production. The present invention satisfies this need.
Briefly, and in general terms, the present invention is directed to a fuel cell having an electrode or catalyst formed from a nano-carbon material, such as fullerene, carbon nanotube, carbon nanohorn, carbon nanofiber and metal encapsulated fullerene. Such an encapsulated fullerene may include a metal from the platinum metal family, including platinum, palladium, rhodium, iridium, osmium and ruthenium. The present invention is applicable to a sandwich-type electrolyte fuel cell, having a first electrode, a second electrode formed from a nano-carbon material and an ion exchange membrane positioned between the first electrode and the second electrode. The efficiency of the fuel cell may be increased by applying external energy to the electrode and/or catalyst.
The present invention relates to fuel cells utilizing hydrogen as the fuel and oxygen containing air as the oxidant. An improvement over previously known fuel cells is that at least one electrode or the catalyst is formed from a hydrogen storable carbon material, such as fullerenes, carbon nanotubes, carbon nanohorns, nanofibers, metal encapsulated fullerenes. Such a fuel cell may include a cationic membrane positioned between the cathode and anode. To reduce the cost of the catalyst, fuel cells constructed according to the present invention may not use platinum at all, or may use platinum in very small amounts.
The present invention further includes an improved method for generating electricity from a fuel cell having a first electrode and a second electrode, such that at least one electrode is formed from a nano-carbon material. An ion exchange membrane may be positioned between the first electrode and the second electrode. Oxygen is directed to the one electrode, and hydrogen is directed to the other electrode. To increase the efficiency of the fuel cell, the electrode containing nano-carbon material is irradiated with blue color diode light, or electric current is directed to the nano-carbon electrode.
Other features and advantages of the invention will become apparent from the following detailed description.